1. Field of the Invention
The present invention relates generally to the processing of semiconductor substrates, and more particularly, the suppression of current arcing near the substrate material.
2. Description of the Related Art
In the field of semiconductor processing, substrates are processed in plasma processing chambers by introducing a process gas into the reaction chamber of the plasma processing chamber and exciting the gas to a plasma state with the application of a radio frequency (RF) field.
The semiconductor substrates are commonly held in place on a substrate support within the reaction chambers using devices such as mechanical clamps or electrostatic clamps (ESC). Process gases are introduced into the chamber using various methods, one method being the use of a gas distribution plate (GDP) mounted at the top of an etching chamber. To excite the gas to a plasma state an RF field is applied to the process gas via electrodes using techniques such as transformer coupled plasma (TCP), also called inductively coupled plasma (ICP), and electron-cyclotron resonance (ECR).
Because of the high power used to generate the RF field and the requirement that an even plasma field is generated to provide consistent formation of high aspect ratio features on the entire substrate, it is highly desirable that current within the chamber follow a path to ground. Drawing current from the reaction chamber toward the grounded body of the plasma processing chamber wall is an example of a preferred path to ground presently being used. Current not following the desired path to ground and arcing near the substrate can create disturbances in the plasma which is detrimental to forming uniform features on the entire substrate and can result in reduced yields.
Concurrent with the need to suppress arcing of current near the substrate surface is the need to allow access for regular maintenance of the components within the plasma processing chamber. The particle and by-product producing nature of the processing that occurs within the reaction chamber requires periodic cleaning and replacement of worn or damaged components. Minimizing the time required for cleaning and maintenance means there can be maximum output from the plasma processing chamber.
Aluminum and aluminum alloys are typically used for walls, electrodes, fasteners and other components of the reaction chamber. To minimize the possibility of undesirable stray arcing near the substrate, materials with high dielectric properties such as ceramics and quartz are used to isolate metal components.
Because of the brittle nature of ceramics and quartz, screw covers made from those materials cannot completely electrically isolate countersunk fasteners without making the fasteners unserviceable or requiring the breaking of the screw cover to access the fasteners. A typical solution is to use quartz screw covers which have an outside diameter small enough so the screw cover cannot become wedged in the countersink. This solution allows access to the underlying fasteners however, the loose fit of the screw cover means they can be displaced during cleaning of the chamber either by getting blown from the countersink with compressed clean dry air or pulled out of the countersink and into a vacuum cleaner.
Both problems require locating and replacing the screw covers which can lead to prolonged downtime of the plasma processing chamber and increased maintenance costs. Additionally, the loose fit between the screw covers and countersink can promote an alternate path to ground via the metallic fastener within the countersink. Current not following the intended path to ground near the substrate has the potential to create arcing that would disturb the plasma and result in non-uniform etching.
In view of the forgoing, there is a need for improved isolation to suppress stray arcing within the etching chamber while also reducing chamber downtime due to parts being lost during regular maintenance.